A radiation image recording and reproducing method utilizing a stimulable phosphor described, for instance, in U.S. Pat. No. 4,239,968, is now practically employed. In the method, a radiation image storage panel comprising a stimulable phosphor (i.e., stimulable phosphor sheet) is employed, and the method comprises the steps of causing the stimulable phosphor of the panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a considerably smaller dose, as compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen. Further, the radiation image recording and reproducing method using a stimulable phosphor is of great value especially when the method is employed for medical diagnosis.
The radiation image storage panel employed in the above-described method comprises a stimulable phosphor layer which may be provided on a support. The stimulable phosphor layer generally comprises a binder and a stimulable phosphor (in the form of particles). The stimulable phosphor emits light (that is, gives stimulated emission) when it is excited with stimulating rays after it is exposed to radiation such as X-rays.
The stimulable phosphor layer generally comprises stimulable phosphor particles and a binder. Stimulable phosphor layers of other types are also known. For instance, a stimulable phosphor layer comprising agglomerated stimulable phosphor particles and no binder can be prepared by a sintering method or a vacuum deposition method. The agglomerated stimulable phosphor layer can contain a polymer, if desired. Any of radiation image storage panels having these stimulable phosphor layers can be employed in the above-described radiation image recording and reproducing method.
Further, a transparent film of polymer material is generally placed on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock. The protective film can be arranged, for instance, by coating a solution of a transparent organic polymer such as a cellulose derivative or polymethyl methacrylate on the phosphor layer, or by fixing a beforehand prepared polymer film such as a polyethylene terephthalate film on the phosphor layer with an adhesive. The coated protective layer can be readily prepared by coating a solution of polymer material on the phosphor layer, and the coated protective layer is firmly fixed on the phosphor layer.
In the radiation image recording and reproducing method, the radiation image storage panel is repeatedly employed in the steps of radiation of X-rays (for recording of radiation image), irradiation of stimulating rays (for reading out of the recorded radiation image), and exposure to erasing light (for erasure of residual radiation image). Between these steps, the storage panel is transferred by conveyors such as belts and rollers in the apparatus for performing the radiation image recording and reproducing method. When these steps are repeated, the coated protective layer of the storage panel is apt to be stained or to receive abrasions or scratches on its surface. The stains, abrasions, and/or scratches produced on the surface of the protective layer cause deterioration of image quality of a reproduced radiation image. The radiation image storage panel naturally is desired to give a reproduced radiation image of high quality (such as high sharpness and improved graininess). Therefore, production of stains, abrasions and scratches on the surface of the protective layer should be avoided.
Japanese Patent Provisional Publication No. 2(1990)-193100 (corresponding to U.S. patent application Ser. No. 08/469,761) describes a protective film of a fluororesin which is soluble in an organic solvent and is coated on a stimulable phosphor layer of a radiation image storage panel. The protective film of a fluororesin can effectively reduce the production of stains, abrasions and scratches.
U.S. Pat. No. 5,227,253 discloses a radiation image storage panel having a protective film which is produced from a mixture of a film-forming resin (such as a fluororesin) and an oligomer having a polysiloxane skeleton or a perfluoroalkyl group. The protective film of a mixture of the fluororesin and others can more effectively reduce the production of stain, abrasions and scratches.
U.S. patent application Ser. No. 08/582,502 describes a radiation image storage panel comprising a stimulable phosphor layer and a protective film placed thereon, wherein the protective film comprises a film of plastic material and a layer of a fluororesin-containing resin composition coated thereon, the coated layer having been prepared by coating on the film of plastic material a solution of a resin composition containing not less than 30 wt. % of a fluororesin and drying thus coated solution layer. This radiation images storage panel is described to have not only favorable anti-staining, anti-abrasion and anti-scratch properties but also sufficient physical strength to keep the protective film from production of cracks therein.